1. Field of the Invention
The present invention relates to an analog data-input device provided with a pressure sensor of a microelectromechanical type, in particular for use in a portable apparatus, such as a mobile phone, to which the ensuing description will make explicit reference, without this implying any loss of generality.
2. Description of the Related Art
As is known, latest-generation mobile phones offer a plurality of advanced functions, such as e-mail and internet managing, displaying of electronic documents, acquiring and displaying of images, in addition to “standard” functions, such as managing of telephone books, phone calls and text messages. Graphic user interfaces (GUIs) enable simple and effective management of the various functions, via data-input devices (generally called Trackpoints®) integrated in the mobile phones. The data-input devices enable scrolling of lists, making of selections, moving of a cursor displayed on the screen, or in general generation of actions within the graphic interface.
Data-input devices generally comprise an actuator element that can be actuated by a user, and a sensor mechanically coupled to the actuator element to detect its actuation and generate corresponding electrical signals. Such electrical signals, possibly amplified and filtered, are acquired by an electronic control circuit of the mobile phone, which thus generates the corresponding action within the graphic interface (for example, cursor displacement, or scrolling of a list).
In detail, the actuator element comprises one or more push-buttons, for example four arranged to form a cross. A direction of displacement within the graphic interface (for example, “Up”, “Down”, “Right”, “Left”) corresponds to each one of the push-buttons. Alternatively, instead of the push-buttons, the actuator element can comprise a single pin-shaped element (joystick), which is mobile in a number of directions.
The sensor comprises one or more sensitive elements, which can be of a digital type, or of an analog type. The sensitive elements of a digital type are switches, which are mechanically coupled to the actuator elements and close upon their actuation (for example, upon the pressure of a corresponding push-button, or else upon the displacement of the joystick in the corresponding direction). The sensitive elements of an analog type are piezoelectric or piezoresistive and comprise a mechanical element and an interface electronic circuit external to the mechanical element. The mechanical element undergoes a deformation following upon actuation of the actuator elements and generates an electrical quantity corresponding to the undergone deformation (a variation of electrical charge or of a resistivity). The interface electronic circuit generally comprises charge-amplifier circuits (in the case of piezoelectric sensitive elements), or bridge circuits (in the case of piezoresistive sensitive elements), and generates an electrical signal proportional to the deformation undergone by the mechanical element, which is acquired by the control circuit of the mobile phone.
If the data-input devices comprise sensitive elements of a digital type, the only information available to the control circuit of the mobile phone is the binary closing or opening state of the switches. Consequently, it is not possible to have a flexible control of the corresponding actions within the graphic interface; for example, it is possible to generate a displacement of a cursor in one or more directions, but it is not possible to regulate its speed of displacement. For this reason, operations such as the scrolling of a phone book, or else the zoom of an image are particularly laborious and far from immediate in so far as they require prolonged pressure on one and the same push-button, or else the displacement of the joystick in the same direction for a long time interval.
Instead, if the data-input devices comprise sensitive elements of an analog type, the control circuit of the mobile phone receives not only the information regarding the detection of an actuation of an actuator element, but also the information regarding the intensity of said actuation. Consequently, the control circuit provides a more flexible control of the actions generated within the graphic interface. For example, not only does it impart on the cursor a displacement in one or more directions, but also regulates its speed of displacement on the basis of the force with which the actuator elements have been actuated (and hence the amount of the corresponding deformation of the sensitive elements).
Known data-input devices comprising sensitive elements of an analog type have, however, the disadvantage of entailing a greater occupation of area and a greater complexity of implementation, both due to the presence of the mechanical element and the interface electronic circuit external to the mechanical element, and to the need for providing the corresponding electrical connections. Consequently, said devices are not particularly suited to integration in portable apparatuses, such as mobile phones.